External repositories don't regenerate in response to XCode changes

[Silic0nS0ldier]

Description of the problem / feature request:

An external repositories which uses host state as an input did not regenerate in response to changes. In this case XCode.

Feature requests: what underlying problem are you trying to solve with this feature?

NA

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

On a machine without XCode (App Store) installed...

1. Clone Bazel repo
2. Run bazel build //src:bazel-dev
3. Observe build failure (due to missing SDK, I haven't ruled out my device being in a bad state)
4. Install XCode (App Store)
5. Run bazel build //src:bazel-dev
6. Observe build failure due to generated external repositories being out of sync

   ERROR: /private/var/tmp/_bazel_jordan/334f33179bc015d52bb8bdf09a360987/external/com_google_protobuf/BUILD:161:11: Compiling src/google/protobuf/io/zero_copy_stream.cc failed: undeclared inclusion(s) in rule '@com_google_protobuf//:protobuf_lite':
   this rule is missing dependency declarations for the following files included by 'src/google/protobuf/io/zero_copy_stream.cc':
   '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/string'
   '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__config'
   ...
   

7. Run bazel clean --expunge (or bazel sync --configure as per External repositories don't regenerate in response to XCode changes #14551 (comment))
8. Run bazel build //src:bazel-dev
9. Observe successful build

What operating system are you running Bazel on?

MacOS

What's the output of bazel info release?

release 6.0.0-pre.20211215.3

If bazel info release returns "development version" or "(@Non-Git)", tell us how you built Bazel.

NA

What's the output of git remote get-url origin ; git rev-parse master ; git rev-parse HEAD ?

https://github.com/Silic0nS0ldier/bazel.git
b92d5c3ca209ac3495b72fdf488eb9291455a8e2
26d4aadaf4006efd6ff20004aa1430e97263b30c

Have you found anything relevant by searching the web?

No, I knew what was causing the initial build issues when I saw it. Resolving the missing dependency issues revealed the external repository caching issue.

Any other information, logs, or outputs that you want to share?

Nope

[Wyverald]

This is WAI, I think. We don't watch for changes in files outside the main repo and external repos, and I don't think there's a reasonable way to do so.

[fmeum]

bazel sync --configure should be a much cheaper way to pick up the local changes than bazel clean --expunge.

[brentleyjones]

There is a way to fix this, by using apple_host_system_env, as shown by @jerrymarino here: #8902 (comment)

Edit: maybe only wrapped_clang is updating in that change. But I wonder if something similar can cause the whole thing to be regenerated.

[keith]

We work around this in 2 ways today.

1. Our bazel wrapper script always passes DEVELOPER_DIR in the environment, so if the path ever changes, things are recomputed
2. We hack the Xcode version into the environment as well using one of the variables that doesn't matter for our build, but the crosstool implementation respects as requiring a reconfigure, this handles the case where users update Xcode at the same path so only the version changes, which is quite common. We put the output of xcodebuild -version in that.

[github-actions]

Thank you for contributing to the Bazel repository! This issue has been marked as stale since it has not had any activity in the last 1+ years. It will be closed in the next 14 days unless any other activity occurs or one of the following labels is added: "not stale", "awaiting-bazeler". Please reach out to the triage team (@bazelbuild/triage) if you think this issue is still relevant or you are interested in getting the issue resolved.